1. Field of the Invention
The present invention relates to calibration methods of determining servo parameters for reading and writing an optical disc, and more particularly, to calibration methods capable of determining optimal servo parameters for a blank optical disc.
2. Description of the Prior Art
A rewritable drive is popularly used for backing up important data. Precise writing and reading data on the optical disc by the rewritable drive secures the accuracy of the data stored in the optical disc.
Please refer to FIG. 1, which is a block diagram of a servo system 100 in a rewritable drive, for illustrating how a writing procedure and a reading procedure are performed by the rewritable drive. As shown in FIG. 1, an optical disc 101 is loaded and rotated by a spindle 103.
In the reading procedure, an optical pickup unit (OPU) 102 is utilized for reading data stored on the optical disc 101. A radio frequency (RF) unit 104 receives and processes RF signals read from the optical disc 101, and a read channel 105 converts output signals of the RF unit 104 from analog to digital. A decoder 106 decodes the digital signals outputted from the read channel 105 into plain data, and it is capable of generating one or more data quality indexes, for example, PI (Parity Inner) error rate, jitter value, beta value, and M14 parameter.
M14 parameter represents a reflection difference between a 14T pit and a 14T land, and therefore, M14 is the maximum amplitude of the RF signal. This parameter M14 can be used to determine an optimal write power by referencing a characteristic curve of a reflection difference M14 versus a recording power.
In the writing and reading procedures, it is desirable to maintain a low PI error rate, a low jitter value, and a large M14 parameter. For the beta value, it is desirable to keep the beta value as close to the target beta value as possible.
In the writing procedure, plain data is first encoded by an encoder 109. A write strategy generator 108 calculates and generates adequate writing pulses based on the data encoded by the encoder 109, and a laser driver (LD) 107 emits laser beam onto the optical disc 101. The tracking error (TE) and focusing error (FE) generated by the RF unit 104 are sent to a digital signal processor (DSP) 111 for calculating a control force for a power driver 110. The power driver 110 controls the movement of the OPU 102 by a focus control signal and a track control signal, and the power driver 110 also generates a spindle control signal for the spindle 103.
However, if the rewritable drive reads a blank optical disc, due to the absence of data for calibrating the reading parameter (such as a read focusing error (FE) offset/bias or a read tracking error (TE) offset/bias), the rewritable drive may utilize an improper reading parameter to perform write servo signal calibration and optimum power calibration (OPC), where the fact results in acquiring an improper writing parameter or an improper writing power. The improper writing parameter or the improper writing power increases the bit error rate, and thus degrades the recording quality.
Note that the write/read FE offset indicates a focus location of a focus servo in writing/reading, the write/read TE offset indicates a track location of a tracking servo in writing/reading, the write/read FE bias indicates a bias added on a focus servo control force in writing/reading, and the write/read TE bias indicates a bias added on a tracking servo control force in writing/reading.